locating the pop

when playing today i would occasionaly get a loud pop from my amp, the same sorta sound you get if you turn the preamp on when the power amps already on, or if you unplug the bass when the amps still on.

there are 3 new things in my setup
1. new bass (MTD kingston)
2. new pre to power amp cable
3. new power cables

i can't replace 2 or 3 to see if they're the problem, and the pop only happened once every 5 minutes or so, one time there was 25 minutes without a pop.